The differential diagnosis of median canaliform nail dystrophy includes habit tic deformity (Table). It also includes other causes of longitudinal splits in the nail plate such as direct trauma to the nail unit. In addition, digital mucous cyst (synovial cyst), lichen striatus, nail-patella syndrome, pterygium, Raynaud disease, and trachyonychia are other conditions in which a longitudinal nail defect has been described.5,7,30,31
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Habit tic deformity is usually present in one or both thumbnails and results in alteration of the normal nail growth. It is caused by the constant or habitual rubbing of the thumb's proximal nail fold by the tip of the second digit. The subsequent damage to the nail matrix causes clinical changes in the nail plate that appear different than those of median canaliform nail dystrophy. The habit tic deformity produces transverse ridges along the central nail plate depression instead of a longitudinal groove with lateral projections. The depth of the central nail plate canal depends on the intensity of the inflicted trauma by the index finger to the matrix of the thumbnail. In addition, the lunula may appear red and enlarged.9,29 Also, the proximal nail fold may be swollen.5,13
Median canaliform nail dystrophy has occasionally been described to periodically disappear; often, the nail defect reappears in these individuals.4-7,13,15,17,24 In some patients, the central nail defect is replaced by a longitudinal ridge5,6; however, in most patients, such as ours, the condition does not resolve spontaneously. Keeping the nail length short and buffing the surface of the nail can prevent the edge of the nail plate from catching on clothing and other objects.5 Covering the nail plate with tape or a nail wrap also can aid in ensuring that jagged edges are not present.4,7
Conclusion
Familial median canaliform nail dystrophy has rarely been described. Our patient had adult onset of his condition involving both thumbnails with associated red macrolunula. His brother and his mother also experienced the same nail dystrophy. Including our patient and his family, median canaliform nail dystrophy has only been reported in 4 families. The mode of inheritance for median canaliform nail dystrophy in these families remains to be determined.